Heretofore, top entry ball valves have been provided in which the valve seats have been inserted about the flow passages and removed from the valve chamber from the access opening to the valve chamber provided upon removal of the bonnet or top cover plate. Thus, upon removal of the bonnet closing the access opening, the seats and ball closure member may be installed in or removed from a seated position about the inlet and outlet flow passages in fluid communication with the valve chamber.
As shown in U.S. Pat. No. 3,771,545 dated Nov. 13, 1973, a top entry ball valve is illustrated in which a ball valve member is installed within a valve chamber along with upstream and downstream seats upon removal of the upper cover plate or bonnet. Seat recesses are provided about the inlet and outlet flow passages and the seats are positioned within the seat recesses. As a relatively long length seat is required if the seat is inserted within a recess, a sufficient clearance must be provided between the ball closure member and the valve body adjacent the recess to permit the seat to pass the ball member. For this purpose the valve seats have generally spherical opposed end surfaces for passing the position of the valve chamber body or wall adjacent the recess for the seat. The seat has an inner spherical seating surface which conforms to the outer spherical surface of the ball closure member so that the seat may be easily moved along the outer spherical surface of the ball closure member. The seats shown in U.S. Pat. No. 3,771,345 are two piece seats and are adapted to be slid along the spherical surface of the ball into a recessed position with the seat recesses. The ball valve member is trunnion mounted.
U.S. Pat. No. 4,637,421 dated Jan. 20, 1987 also shows a top entry floating ball valve in which spacer rings are mounted against resilient seats in seat recesses in the valve body. The spacer rings having a concentric inner and outer spherical surfaces with the inner spherical surface conforming to the outer surface of the ball closure member so that it may slide and be easily moved along the surface of the ball closure member for proper positioning. Upstream and downstream sealing members are provided within the seat recesses of the valve body. A relatively large valve chamber is provided to receive the ball closure member and spacers and a large entrance or access opening to the valve chamber is provided by the upper cover plate.